<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>ajax介绍</title>
</head>
<body>
    <script>
        console.log(1);
        console.log(2);
        console.log(3);
        // 异步，在6秒等待时，4已经打印出来了
        setTimeout(function () {
            console.log(5);
        },6000);
        console.log(4);
    </script>
</body>
</html>